title: Caffeine junkie: an unprecedented glutathione S-transferase-dependent oxygenase required for caffeine degradation by Pseudomonas putida CBB5.
abstract: Caffeine and other N-methylated xanthines are natural products found in many foods, beverages, and pharmaceuticals. Therefore, it is not surprising that bacteria have evolved to live on caffeine as a sole carbon and nitrogen source. The caffeine degradation pathway of Pseudomonas putida CBB5 utilizes an unprecedented glutathione-S-transferase-dependent Rieske oxygenase for demethylation of 7-methylxanthine to xanthine, the final step in caffeine N-demethylation. The gene coding this function is unusual, in that the iron-sulfur and non-heme iron domains that compose the normally functional Rieske oxygenase (RO) are encoded by separate proteins. The non-heme iron domain is located in the monooxygenase, ndmC, while the Rieske [2Fe-2S] domain is fused to the RO reductase gene, ndmD. This fusion, however, does not interfere with the interaction of the reductase with N1- and N3-demethylase RO oxygenases, which are involved in the initial reactions of caffeine degradation. We demonstrate that the N7-demethylation reaction absolutely requires a unique, tightly bound protein complex composed of NdmC, NdmD, and NdmE, a novel glutathione-S-transferase (GST). NdmE is proposed to function as a noncatalytic subunit that serves a structural role in the complexation of the oxygenase (NdmC) and Rieske domains (NdmD). Genome analyses found this gene organization of a split RO and GST gene cluster to occur more broadly, implying a larger function for RO-GST protein partners.
authors.affiliation: Center for Biocatalysis and Bioprocessing and Department of Chemical and Biochemical Engineering, The University of Iowa, Coralville, Iowa, USA.
authors.forename: Ryan M
authors.initials: RM
authors.lastname: Summers
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Seffernick
authors.forename: Erik M
authors.initials: EM
authors.lastname: Quandt
authors.forename: Chi Li
authors.initials: CL
authors.lastname: Yu
authors.forename: Jeffrey E
authors.initials: JE
authors.lastname: Barrick
authors.forename: Mani V
authors.initials: MV
authors.lastname: Subramanian
mesh_terms: D001711:Biotransformation; D002110:Caffeine / Q000378:metabolism*; D002244:Carbon / Q000378:metabolism; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D023061:Gene Order; D005982:Glutathione Transferase / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D005810:Multigene Family; D009584:Nitrogen / Q000378:metabolism; D010105:Oxygenases / Q000235:genetics / Q000378:metabolism*; D016958:Pseudomonas putida / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism*; D017422:Sequence Analysis, DNA; D026801:Synteny
chemical_list: D004269:DNA, Bacterial; D002110:Caffeine; D002244:Carbon; D010105:Oxygenases; D005982:Glutathione Transferase; D009584:Nitrogen